1. Field of the Invention
This invention relates to wire carriers having a knitted stitching used as backing for elastomeric weather seals in automotive and other applications.
2. Background Information
Knitted wire carriers are commonly used in the area of automotive weather seals, among other uses. Generally, such carriers consist of a continuous wire weft formed into a zigzag pattern with rounded ends. The ends join together a series of approximately parallel weft segments (limbs) upon which a plurality of warp threads are knitted. This type of knitted wire carrier is used as a reinforcing frame for elastomeric seals that are produced by extrusion and other continuous-forming processes. Such seals are often used in automotive and other vehicle applications.
The manufacture of extruded weather seals involves the application of substantial forming heat and pressure to the wire carrier. The warp threads in many examples is applied in three clusters or strips, all of which are designed to maintain the zigzag wire weft the appropriately spaced orientation during the formation process. Absent these warp threads, the wire would tend to stretch and deform, generating an inferior or unusable finished seal product. However, even where a plurality of clustered warp threads are firmly knitted to a zigzag wire weft, problems may still arise during seal formation. The flow of elastomeric seal material and the basic motion of the knitted wire carrier through the formation machinery may cause the warp threads to migrate along the weft at various points. Thus, the end-mounted warp becomes misaligned and migrates inward toward the center while a centrally mounted warp (where used) may migrate to the side.
One approach for dealing with the problem of warp migration along the weft wire is to coat the entire knitted structure in polymer prior to seal extrusion. Besides the added cost of an additional manufacture step, this approach is disadvantaged in that it generates a less flexible structure in which the polymer coating may flake off (due to flexure of the carrier) during or after seal formation. These flakes can dirty or damage the seal-forming machinery, among other disadvantages.
Another approach to securing warp threads against migration along the wire is described in U.S. Pat. No. 5,416,961 entitled KNITTED WIRE CARRIER HAVING BONDED WARP THREADS AND METHOD FOR FORMING SAME, by Paul M. Vinay the teachings of which are expressly incorporated herein by reference. This patent teaches the use of a meltable or shrinkable filament, formed entirely of a material such as polypropylene, which melts to the carrier and/or shrinks to draw the warp filaments tightly together upon application of heat. However, using such a filament subjects the warp and carrier to significant shrinkage and may tend to deform the knitted structure, particularly after continued application of heat.
Accordingly, it is desirable to provide a knitted wire carrier that limits or eliminates the possibility of warp migration along the wire, but does not exhibit distorting or deforming levels of shrinkage.